Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the colon and small intestine, principally including Crohn's disease and ulcerative colitis, with other forms of IBD representing far fewer cases (e.g., collagenous colitis, lymphocytic colitis, diversion colitis, Behçet's disease and indeterminate colitis). Pathologically, Crohn's disease affects the full thickness of the bowel wall (e.g., transmural lesions) and can affect any part of the gastrointestinal tract, while ulcerative colitis is restricted to the mucosa (epithelial lining) of the colon and rectum. Graft-versus-host disease (GVHD) is an immune-related disease that can occur following an allogeneic tissue transplant. It is commonly associated with stem cell or bone marrow transplants, but GVHD also applies to other forms of tissue graft. In GVHD immune cells of the tissue graft recognize the recipient host as foreign and attack the host's cells.
It has long been recognized that IBD and GVHD are diseases associated with increased immune activity. The causes of IBD, while not well understood, may be related to an aberrant immune response to the microbiota in genetically susceptible individuals. IBD affects over 1.4 million people in the United States and over 2.2 million in Europe and is on the increase. With both environmental and genetic factors playing a role in the development and progression of IBD, response to current treatments (e.g., anti-inflammatory drugs, immune system suppressors, antibiotics, surgery, and other symptom specific medications) are unpredictable.
Similarly, a fundamental feature of GVHD is increased immune activity. As yet, the pathophysiology underlying GVHD is not well understood. It is a significant cause of morbidity and mortality following allogenic haematopoietic stem-cell transplantation and thus the focus of much ongoing research. Despite the advances in understanding the pathophysiology (e.g., predisposing factors), a standardized therapeutic strategy is still lacking. Currently both acute and chronic forms of GVHD are treated using corticosteroids (e.g., anti-inflammatory treatments). There is a need for new approaches to treating IBD and GVHD.